diff options
| author | Tobias Waldekranz | 2022-01-28 17:26:49 +0100 |
|---|---|---|
| committer | David S. Miller | 2022-01-31 11:29:12 +0000 |
| commit | 35da1dfd94847c5f1ac04ce5b5002b888c3f36ec (patch) | |
| tree | fdefec27b2f1a8e1052d89441b7b16a731a73202 | |
| parent | 0da8aa00bfcfeb3f4e6537dd8e2001e0727ba549 (diff) | |
net: dsa: mv88e6xxx: Improve performance of busy bit polling
Avoid a long delay when a busy bit is still set and has to be polled
again.
Measurements on a system with 2 Opals (6097F) and one Agate (6352)
show that even with this much tighter loop, we have about a 50% chance
of the bit being cleared on the first poll, all other accesses see the
bit being cleared on the second poll.
On a standard MDIO bus running MDC at 2.5MHz, a single access with 32
bits of preamble plus 32 bits of data takes 64*(1/2.5MHz) = 25.6us.
This means that mv88e6xxx_smi_direct_wait took 26us + CPU overhead in
the fast scenario, but 26us + 1500us + 26us + CPU overhead in the slow
case - bringing the average close to 1ms.
With this change in place, the slow case is closer to 2*26us + CPU
overhead, with the average well below 100us - a 10x improvement.
This translates to real-world winnings. On a 3-chip 20-port system,
the modprobe time drops by 88%:
Before:
root@coronet:~# time modprobe mv88e6xxx
real 0m 15.99s
user 0m 0.00s
sys 0m 1.52s
After:
root@coronet:~# time modprobe mv88e6xxx
real 0m 2.21s
user 0m 0.00s
sys 0m 1.54s
Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
| -rw-r--r-- | drivers/net/dsa/mv88e6xxx/chip.c | 13 | ||||
| -rw-r--r-- | drivers/net/dsa/mv88e6xxx/smi.c | 11 |
2 files changed, 19 insertions, 5 deletions
diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c index 58ca684d73f7..1023e4549359 100644 --- a/drivers/net/dsa/mv88e6xxx/chip.c +++ b/drivers/net/dsa/mv88e6xxx/chip.c @@ -86,12 +86,16 @@ int mv88e6xxx_write(struct mv88e6xxx_chip *chip, int addr, int reg, u16 val) int mv88e6xxx_wait_mask(struct mv88e6xxx_chip *chip, int addr, int reg, u16 mask, u16 val) { + const unsigned long timeout = jiffies + msecs_to_jiffies(50); u16 data; int err; int i; - /* There's no bus specific operation to wait for a mask */ - for (i = 0; i < 16; i++) { + /* There's no bus specific operation to wait for a mask. Even + * if the initial poll takes longer than 50ms, always do at + * least one more attempt. + */ + for (i = 0; time_before(jiffies, timeout) || (i < 2); i++) { err = mv88e6xxx_read(chip, addr, reg, &data); if (err) return err; @@ -99,7 +103,10 @@ int mv88e6xxx_wait_mask(struct mv88e6xxx_chip *chip, int addr, int reg, if ((data & mask) == val) return 0; - usleep_range(1000, 2000); + if (i < 2) + cpu_relax(); + else + usleep_range(1000, 2000); } dev_err(chip->dev, "Timeout while waiting for switch\n"); diff --git a/drivers/net/dsa/mv88e6xxx/smi.c b/drivers/net/dsa/mv88e6xxx/smi.c index 282fe08db050..728ef3f54ec5 100644 --- a/drivers/net/dsa/mv88e6xxx/smi.c +++ b/drivers/net/dsa/mv88e6xxx/smi.c @@ -55,11 +55,15 @@ static int mv88e6xxx_smi_direct_write(struct mv88e6xxx_chip *chip, static int mv88e6xxx_smi_direct_wait(struct mv88e6xxx_chip *chip, int dev, int reg, int bit, int val) { + const unsigned long timeout = jiffies + msecs_to_jiffies(50); u16 data; int err; int i; - for (i = 0; i < 16; i++) { + /* Even if the initial poll takes longer than 50ms, always do + * at least one more attempt. + */ + for (i = 0; time_before(jiffies, timeout) || (i < 2); i++) { err = mv88e6xxx_smi_direct_read(chip, dev, reg, &data); if (err) return err; @@ -67,7 +71,10 @@ static int mv88e6xxx_smi_direct_wait(struct mv88e6xxx_chip *chip, if (!!(data & BIT(bit)) == !!val) return 0; - usleep_range(1000, 2000); + if (i < 2) + cpu_relax(); + else + usleep_range(1000, 2000); } return -ETIMEDOUT; |